matlab - repmat function does not work properly -

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let consider following situation,for instance have given matrix , want make 0 centered matrix in columns,so

a=rand(4,3)  =      0.6948    0.4387    0.1869     0.3171    0.3816    0.4898     0.9502    0.7655    0.4456     0.0344    0.7952    0.6463

now 2 method works properly

a-repmat(mean(a),size(a,1),1)  ans =      0.1957   -0.1565   -0.2553    -0.1820   -0.2137    0.0476     0.4511    0.1703    0.0035    -0.4647    0.1999    0.2042

and also

bsxfun(@minus,a,mean(a))  ans =      0.1957   -0.1565   -0.2553    -0.1820   -0.2137    0.0476     0.4511    0.1703    0.0035    -0.4647    0.1999    0.2042

but somehow following method not work

b=mean(a)  b =      0.4991    0.5953    0.4421   a-repmat(b,1,4)  ans =       0     0     0     0     0     0     0     0     0     0     0     0

i have tried transpose but

a-repmat(b,1,4)' error using  -  matrix dimensions must agree.

also have tried following

a-repmat(b,1,3)' error using  -  matrix dimensions must agree.  >> a-repmat(b,1,3) error using  -  matrix dimensions must agree.  problem of  failure of method?

you not using proper syntax repmat function

in example ,you need create matrix of size 4 x 3 using repmat

now call repmat(a,k,j) repeats matrix a k times along first dimension (i.e vertically) , j times along second dimension (i.e, horizontally).

here, need repeat matrix mean 4 times in first dimension , 1 time in second dimension .

hence, correct call repmat repmat(mean,4,1) 

repmat(b,4,1)  ans =      0.4991    0.5953    0.4421     0.4991    0.5953    0.4421     0.4991    0.5953    0.4421     0.4991    0.5953    0.4421

it looks need know why method failing

repmat(b,1,4) %// returns 1x12 matrix while 3x4 matrix hence dimensions not agree while using @minus ans =      0.4991    0.5953    0.4421   0.4991    0.5953    0.4421   0.4991    0.5953    0.4421   0.4991    0.5953    0.4421

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